Combustion plants emit large amount of flue gas containing fly ash and harmful, acidic gasses, such as SO2. Therefore, to avoid undesired impact on the environment, combustion plants usually have installed flue gas desulfurization systems to reduce SO2 emission.
A particular attractive way of removing acidic components from a flue gas is provided by a spray dryer absorber (SDA). In an SDA acidic gasses are absorbed in an absorbent sprayed into the flue gas. Typically, the flue gas is introduced into a spray dryer absorption chamber and contacted with a fine spray of absorbent slurry, such as an aqueous suspension of burned lime. A significant part of the acidic components in the flue gas are rapidly absorbed into the alkaline droplets and water is evaporated simultaneously. The gas distribution, slurry flow rate and droplet size are controlled such that the droplets are dried to a fine powder.
The conventional design of the SDA chamber includes an upper cylindrical part combined with a lower cone part. Examples of this design are shown in U.S. Pat. No. 4,279,873 (Niro) and U.S. Pat. No. 4,530,822. The intended function of the cone part was to collect the heavy particles that dropped out of the flue gas stream and to secure a volume for deposits to fall into in case of malfunction, thereby securing a clean gas path through the system.
The present inventors have now realized that a clean gas path could be realized by an alternative design of the SDA chamber saving significant investment in materials. Moreover, the frequent maintenance of the product discharge system in the SDA cone may be dispensed with. It is therefore the aim of the present invention to substantially reduce the construction and maintenance costs of an SDA plant. Lower cost of the SDA system may prompt areas rich in coal of a poor quality to control the air pollution by using a SDA system for treating the flue gas.